The invention relates to improvements in roller conveyors in general, and more particularly to improvements in roller conveyors which are designed to transport discrete commodities, e.g., from a maker to a processing machine or to storage. Still more particularly, the invention relates to improvements in roller conveyors adapted to be utilized for automatic transport of sensitive or highly sensitive commodities which are readily deformable, e.g., as a result of contact with neighboring commodities.
It is already known to assemble a roller conveyor from a desired number of cylindrical idler rollers which extend transversely of the direction of intended transport of commodities and can be engaged from below by an endless belt adapted to be driven by a suitable motor. If the rate of delivery of fresh commodities to the upstream end of the roller conveyor exceeds the rate of removal of commodities at the downstream end, the number of commodities which are carried by the rollers increases and ultimately reaches a value at which the neighboring commodities are likely to actually contact each other. In accordance with a presently known proposal, the roller conveyor is equipped with mechanical jam-responsive switches which disconnect the motor from certain rollers when a portion of the path for the commodities is crowded to a predetermined extent. The switches cause disengagement of the endless belt from the rollers beneath the crowded portion or portions of the path by causing the corresponding portion or portions of the belt to descend and to thus interrupt the torque transmitting connection between the motor and the adjacent rollers. At the same time, one or more brakes are set in operation to immediately prevent further rotation of the rollers which are no longer frictionally engaged by the belt.
A drawback of the just described conventional roller conveyor is that the mechanism for moving selected portions of the belt into and from engagement with the adjacent rollers constitutes a complex, bulky and expensive part of the conveyor. As a rule, such mechanism includes pneumatically or electrically operated parts. The provision of brakes for the rollers which are no longer driven by the belt also contributes to complexity and cost of the roller conveyor. Moreover, the brakes and the mechanism for lifting and lowering selected portions of the belt are not readily accessible so that each inspection, maintenance or repair work involves long stoppages of the entire roller conveyor and of the production line in which the conveyor is put to use.